I disagree that it is just Americans. In real terms language evolves on its own and people tend to imitate the pieces they find useful for one reason or another. I remember living in the old country as the Iron Curtain fell. All of a sudden, adding English words into just about any conversation was a thing to do. Some of it was, because word equivalents were not quite ready yet; some of it was fashion.
I think cop porn is just another language phase in US.